Remote infra-red personal alarm system

ABSTRACT

An infra-red remote personal alarm system consists of a portable transmitter unit (10) which is intended to be worn or to be manually carried by the user, and which is operable by the user at any particular location to transmit an alarm signal in an emergency and which is to be received by a central receiving station (41) so that appropriate action can be initiated in response thereto. The transmitter unit is electrically operable and includes means (15) for transmitting pulsed infra-red alarm signals which can be picked-up by an infra-red signal receiver at the location of the user, and then retransmitted as an oscillating electrical signal via direct wiring (38, 39, 40, 42, 43) to the central receiving station (41) as a warning signal indicative at location monitoring points (43, 44) of the location from which the emergency call has been made. By making the transmitter units capable of transmitting infra-red pulsed warning signals, and suitably designing the receiver units to recognize and to receive the pulse signals for conversion into electrical signals for onward transmission to the central control station, it is possible to obtain transmission units which are robust and reliable in operation. Test facilities are also provided to enable continuous monitoring of the operational status of the transmission units and the receiver units, so as to minimize the risk of initiated emergency action of the transmission units being undetected.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a personal alarm system which comprises aportable transmitter unit to be worn about the person, or hand carried,and which is operable in an emergency to transmit an alarm signal whichis to be received and processed by a central receiving station so thatappropriate action can be initiated in response thereto.

2. Description of the Prior Art

There are many situations in which it is necessary, or advisable, for aportable transmitter unit to be available for use in emergencies, suchas by the occupants of sheltered housing schemes, a warden on routinevisits to such occupants, or medical personnel in hospitals or otherinstitutions. In these situations, it is important, when an emergencycall is received at the central control or command station, that thelocation from which the emergency call has been made is immediatelydiscernable, and therefore it is usual to locate a dedicated receiver ateach location to be monitored e.g. on the wall or ceiling of a room, andfor each dedicated receiver to be connectable in any desired manner e.g.radiowave communication or direct electric line connection to thecentral control station, where the re-transmitted emergency signal willbe indicated at the control station as having come from that particularlocation.

It is known to use ultrasonic personal alarm transmitter units, whichissue ultrasonic signals to be received by a dedicated ultrasonicreceiver at each location which is to be monitored (which thenre-transmits to the central station), but ultrasonic units rely uponcrystal devices, which are not robust, and in fact are rather fragile,so that this can cause problems with regard to reliability. In addition,it is a feature of existing ultrasonic transmitters that they cannotreadily be tested as to their current state of serviceability while inuse, and there is therefore a risk that emergency signals may fail to beissued and/or received.

It is also known to provide each member of staff in a hospital or otherpeople-care type institution with his own radio transmitter unit, foruse in emergencies and which transmits a radio signal which is picked-upby a central receiver, and this gives an indication of the caller, butnot of the location where the caller has made the emergency call.Therefore, the radio transmitter units are not suitable for use insituations in which the users may be located in any one of a number ofdifferent locations when the emergency call has been made.

SUMMARY OF THE INVENTION

The present invention has been developed primarily in connection with apersonal alarm system which is able to indicate the location at which anemergency call has been made, and using means which are more reliablethan ultrasonic transmitter/receiver units of existing systems.

According to the invention there is provided a personal alarm systemwhich comprises a portable transmitter unit to be worn or to be handcarried by the user, and which is operable by the user at any particularlocation to transmit an alarm signal in an emergency, such signal beingreceivable by a central receiving station so that appropriate action canbe initiated in response thereto:

in which the transmitter unit is electrically operable and includesmeans for transmitting pulsed infra-red alarm signals to be monitored byan infra-red signal receiver at the location of use of the transmitterunit, and to be re-transmitted to the central receiving station as awarning signal indicative of the location at which the user has operatedthe transmitter unit.

Thus, the personal alarm system may be used to particular advantage inhospitals, especially hospital casualty departments, and in institutionsfor mentally disturbed or handicapped patients, where attacks on medicalstaff are quite frequent, and in which it is important for the member ofstaff to be able easily to issue an emergency call which will bepicked-up by a suitable receiver at each of any desired monitoringlocations, and for the call to be re-transmitted to the central stationin a form which will indicate immediately the location from which thecall has been made, so that immediate help can be directed to any personunder attack.

It should be apparent, however, that the invention is not restricted tosuch use, and can be employed in any situation in which it is arequirement to be able readily to monitor at a central station thelocation from which an emergency call has been made.

Preferably, the personal alarm system according to the invention is usedin conjunction with a signal receiving system which comprises one ormore of said infra-red receivers, each to be located at a respective oneof a plurality of desired monitoring locations, and master receivingequipment to be located at a central or control receiving station toreceive warning signals re-transmitted from any one of the infra-redreceivers.

If a particular location to be monitored is a particularly large area,it may be desirable for more than one infra-red receiver unit to bepositionable at such location, in order to ensure that any pulsedinfra-red emergency call is received, and then onward-transmitted to thecentral control station. Conveniently, the infra-red receivers are eachwired to a central alarm panel which is able to identify the location ofan active transmitter.

By arranging for each transmitter unit to issue pulsed infra-redsignals, it is possible to design the transmitter unit and thecorresponding infra-red receiver unit so that a predetermined pulsepattern can be readily detected and then recognised, and this willovercome, or at least minimise the risk of any spurious infra-redsignals from triggering an alarm signal to the central control station.

To provide a continual reassurance of a proper operation of thetransmitter system and the receiver system, it is preferred that a testfacility is provided which, by incorporating a low-power transmittercircuit within each receiver unit, enables a complete test of theinstallation to be activated from the central alarm panel. In addition,all wiring associated with the installation is monitored continuously,creating an alarm condition if a wiring fault or break is detected.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of personal alarm system according to the invention willnow be described in detail, by way of example only, with reference tothe accompanying drawings, in which:

FIG. 1 is a side view of a portable transmitter unit of a personal alarmsystem, and which is to be worn or to be hand carried by the user;

FIG. 2 is a view, similar to FIG. 1, illustrating schematically theinternal components of the transmitter unit;

FIG. 3 is an end view of the transmitter unit;

FIG. 4 is a block circuit diagram of the infra-red transmitter unitshown in FIGS. 1 to 3;

FIG. 5 is a block circuit diagram of an infra-red receiver unit formingpart of a receiving system to be used with the portable-transmitter unitof the personal alarm system shown in FIGS. 1 to 4;

FIG. 6 shows graphs of timing diagrams of the operating components ofthe alarm transmitting and alarm receiving systems disclosed herein;and,

FIG. 7 illustrates a circuit diagram of the connections from remoteinfra-red receiver units to a central alarm panel at a central controlstation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIGS. 1 to 3 of the drawings, a portable infra-redtransmitter unit is designated generally by reference 10 and forms partof a personal alarm system, the unit 10 being designed so as to becapable of being worn about the person, or hand carried, according topreference of the user. The transmitter unit 10 is electricallyoperable, having a battery compartment, so that in an emergency it cantransmit an alarm signal which is received initially by any one of aplurality of dedicated receivers arranged at a number of monitoringlocations likely to be visited by the user, and then re-transmitted to acentral receiving station so that appropriate action can be initiated inresponse thereto. At the central receiving station, any incoming warningsignal will be monitored in such a way as to determine the location fromwhich the emergency call has been made by the user with his own personalportable transmitter unit.

The transmitter unit 10 is designed as a compact, lightweight andimpact-resistant unit, having a housing 11 designed to hang freely froma belt or key-ring, by means of a spring-retained pin 12. Thetransmitter unit 10 is activated by withdrawing the housing 11 from theretaining pin 12, and by this action it is ensured that the infra-redbeam which is emitted, as shown by beam profile 13 in FIG. 1, isunimpeded by any articles of clothing. The housing 11 incorporates abattery compartment 14 in which a standard miniature 12 volt battery(VR22) is housed in an anti-vibration manner. The forward end of thehousing 11 is provided with an LED array of infra-red emitters and aninfra-red window, shown schematically by reference 15. The electroniccomponents mounted within the housing 11 are shown in the block circuitdiagram of FIG. 4. As shown in the block diagram of FIG. 4, theelectronic components include an astable multivibrator circuit 16triggered into operation by an activation switch 17, a monostablemultivibrator circuit 18, an infra-red LED driver 19 and an infra-redLED array 20. The astable and monostable multivibrator circuits 16 and18 are arranged to produce a continuous train of five microsecond pulsesat 4.67 millisecond intervals. The pulse train is then fed to driver 19,which is a MOSFET driver, and then to the LED array 20, which comprisesa series-parallel combination of high-power infra-red emitters.Therefore, upon emergency operation of the transmitter units 10, apulsed infra-red output of predetermined pattern can be transmitted, andwhich can be recognised and received by any one of the infra-redreceiver units arranged at the various monitoring locations as required.

Referring now to FIG. 5, this illustrates a block diagram of any one ofthe infra-red receivers. The infra-red receiver comprises a photo diode21 forming an input to the receiver, for receiving pulsed infra-redsignals from any one of the infra-red transmitter units, an infra-reddetector and AMP 22, a hit detector 23, a hit counter 24, a comparator25, a window counter 26, a window generator 27, a window reset 28, amaster reset 29, a window synch 30, a time out error circuit 31, analarm latch 32, a monitoring oscillator 33, ah alarm 34, and a testpulse generator 35.

Infra-red pulses received by photo diode 21 from an active transmitterunit, or from the integral self-test circuit provided by test pulsegenerator 35, are received by the detector 22 and dedicated amplifier ic(SL 486 constrained to fixed-gain operation), and then passed to thesubsequent decoding circuitry. The window generator 27 comprises anoscillator and multi-stage counter, the generated output being aninitial delay of 4.6 milliseconds, followed by a window pulse of 148microseconds. Transmitter pulses fall within successive windows, eachwindow being triggered by the previously received pulse, via the windowreset 28. This synchronisation technique effectively discriminatesagainst any other sources of infra-red radiation which could give riseto spurious signals. The window counter 26 is incremented whenever awindow is generated. The hit detector 23 passes pulses which arrivewithin a time window through to the pulse hit counter 24. The alarmlatch 32 is set when the hit counter reaches a pre-set number, and thealarm signal from alarm 34 remains active until manually reset from thecentral alarm panel at the control station.

The count comparator 25 notifies the master reset circuit 29 of anydiscrepancy between the window and hit counters i.e. when no infra-redpulse is received during a time window. The master reset circuit 29causes a reset of the hit counter 24 and the window counter 26 andinitiates the start of the next time window, via the window reset 28.

The window synchronisation circuit synchronises the generation of timewindows to an incoming pulse train, and this circuit is activeimmediately following a window comparator pulse i.e. following a "miss"in any time window.

The time-out error circuit 31 ensures that a system master reset pulsewill be generated, even in the event of a temporary receivermalfunction. Such malfunctions, although rare, may be caused byelectro-magnetic interference or electrical noise in the installation.

The principles of operation of the components thus far described willnow be described with reference to FIG. 6, which shows three modes ofoperation, illustrated in the timing diagrams of FIG. 6. The diagramsillustrate the pulse characteristics, via lines 1 to 7, in which line 1is the window generator, line 2 is the infra-red detector, line 3 is thecomparator, line 4 is the master reset, line 5 is the window reset, line6 is the window synch, and line 7 is the alarm latch. The three possiblemodes of operation which are normally possible are as follows:

1. Detection of an active transmitter.

The hit detector latch is enabled as each generated window opens. Apulse from an active transmitter sets the latch and fires a monostable.The monostable pulse thereby formed then increments the hit counter,causing a window generator reset and disables the hit detactor latch.During the window delay period, therefore, incoming infra-red pulses arerejected. After the window delay period, the next window opens,incrementing the window counter and re-enabling the hit detector latch.The anticipated transmitter pulse now sets the latch and refires themonostable, which again increments the hit counter and initiates anothertiming cycle. With successive transmitter pulses, the hit and windowcounters increment in steps. The alarm latch is set when the hit counterhas accumulated a preset number of counts.

2. Operation in the dark.

If a window opens and closes without receiving an input pulse, adiscrepancy occurs between the hit and window counters. The comparator,which is sampled at the end of each window cycle, becomes active andgenerates a master reset pulse. This resets the hit and window countersand also resets the window generator. In the absence of infra-redsignals, the circuit will continue to produce empty timing windows andmaster reset pulses.

3. Receiver-transmitter synchronisation.

Following the occurrence of an empty window, an input latch in thewindow synchronisation circuit is enabled by the active comparator. Ifan infra-red pulse arrives during the window delay period, this latch isset and a master reset is generated. Hence, if the pulse is the first ofa train of transmitter pulses, the window generator will be correctlysynchronised to the transmitter frequency.

The system incorporates test facilities, to enable continuousreassurance of safe operation of the system is available.

Thus, each receiver has a test circuitry arranged to generate a lowpower infra-red pulse train at an identical frequency to that of one ofthe transmitter units. The circuit can be activated from the centralalarm panel, so that all receivers in the installation are testedsimultaneously. By simulating an active transmitter, the facilityprovides a complete test of each receiver unit.

Concerning the transmitter units, a test unit, based on a modifiedreceiver circuit, is used to test the output power and pulse repetitionfrequency of each transmitter unit, before issue to personnel.

The infra-red receiver units receive and recognise pulsed infra-redinput signals, derived from operation on emergency call of any one ofthe infra-red transmitter units, and then re-transmits the emergencycall via direct electrical wiring to a central control panel at thecontrol or master station. Thus, each receiver unit transmits anoscillating electrical signal, which is inhibited by the alarm latch,via the alarm signal cable to the central control panel. If theoscillations cease, the central control panel signals an alarm/faultcondition. This system provides a continuous monitoring of the integrityif both the power and the signal cabling of the installation.

Referring finally to FIG. 7 of the drawings, this shows the installationrequirements for connection of the infra-red receivers via direct wiringto the central control panel. For illustration purposes only, tworeceiver units only are shown, comprising receiver 36 and receiver 37,and these are connected to low voltage supply and return cables 38 and39, the installation operating under 13.5 volts supply. A test/resetcable daisy chain 40 also extends to all of the receiver units. A singlecable from each receiver carries an alarm/monitor signal to the centralalarm panel 41, and as shown cable 42 connects receiver 36 to an inputindication point 43 on the control panel, at which an alarm or faultindication can be given, depending upon whether the test facility isbeing operated, or a genuine alarm call has been made from a transmitterunit having its infra-red output accessible to the input of any one ofthe receiver unit(s) at receiver 36. Similarly, cable 43 connectsreceiver 37 to an alarm/fault indication point 44 on the control panel.

The system specification of a preferred embodiment is as follows:

    ______________________________________                                        1. Transmitter                                                                Pulse repetition frequency                                                                        214 Hz                                                    Pulse width         5 μs                                                   Peak wavelength emission                                                                          950 nm                                                    Size                                                                          length              75 mm                                                     diameter            26 mm                                                     Weight (including battery)                                                                        60 g                                                      Battery type        VR-22 or equivalent                                       Battery life (continuous)                                                                         45 minutes approx                                         Infra-red beam profile                                                                            80% power in ± 16.                                     2. Receiver                                                                   Range (line of sight)                                                                             20 meters minimum                                         Power consumption (including                                                                      100 mA approx at 12V                                      indicator led)                                                                ______________________________________                                    

We claim:
 1. A personal alarm system which comprises a portabletransmitter unit (10) to be worn or manually carried by the user, andwhich is electrically operable by the user at any particular location totransmit an alarm signal in an emergency which is to be received by acentral receiving station (41) so that appropriate action can beinitiated in response thereto,the transmitter unit (10) including means(15) for transmitting pulsed infra-red alarm signals to be monitored byan infra-red signal receiver (36, 37) at said location and to bere-transmitted to the central receiving station (41) as a warning signalindicative of the location at which the user has made the emergency callcharacterized in that the infra-red receiver (36, 37) comprisesdiscriminating means for discriminating between spurious infra-redsignals and signals transmitted by the transmission unit (10) thediscriminating means including means for recognizing and detecting apredetermined pulse pattern.
 2. An alarm system according to claim 1,characterized by a plurality of infra-red receivers (36, 37) adapted tobe mounted at a plurality of said locations.
 3. An alarm systemaccording to claim 2, characterized in that said infra-red receivers(36, 37) are connected by electric lines (38, 39, 40, 42, 43) to saidcentral receiving station (41).
 4. An alarm system according to any oneof claims 1 to 3, characterised in that the transmitter unit (10)comprises a housing (11) having a spring-loaded retaining pin (12) forattaching the unit (10) to the user, release of which causes automatictriggering into operation of the unit to emit pulsed infra-red signalsin an emergency.
 5. A personal alarm system according to claim 1 orclaim 2 wherein the discriminating means comprises a detector andamplifier (22) for detecting a pulsed signal from the transmitter unit(10) and decoding circuitry in communication with said detector andamplifier.
 6. A personal alarm system according to claim 5 wherein thedecoding circuitry comprises: a hit detector (23) connected to thedetector and amplifier (22), a hit counter (24) connected to the hitdetector (23); a window counter (26) and window generator 27, connectedto one another and to the hit detector (23); a comparator (25) in serieswith the hit counter (24), and the window counter for detecting anydiscrepancy between the window and the hit counters; a master reset (29)connected to the comparator (25); a window synch (30) connected to thedetector and amplifier (22) and the comparator (25) for synchronisingthe generation of time windows to an incoming pulse train; a time outerror (31) connected to the window generator; an alarm latch (32)connected to the hit counter (24), and a test pulse generator (35) forgenerating test pulses to test the circuit.